1. Field of the Invention
This invention relates to an apparatus for steering or otherwise guiding a payload through the inside of a substantially horizontal pipe. More particularly, this invention relates to an apparatus for transporting instrumentation or other equipment for internal inspection, maintenance and/or repair of an underground pipe, such as a utility pipeline, which apparatus automatically maintains a substantially vertical orientation within the pipe as it moves through the pipe. Typically, the payload is mounted to a support that is pulled or pushed or otherwise motivated along the centerline of the pipe.
2. Description of Related Art
Internal inspection, maintenance and repair of underground utility pipelines is frequently utilized to avoid expensive excavation of the ground surrounding the pipeline. In addition to being expensive, excavation offers the potential for damage to the pipeline resulting, for example, from contact with the excavation equipment.
Tools for internal pipeline inspection perform a wide variety of specific functions, such as geometric surveys, determination of metal loss, and detection of cracks or leaks. Conventional means for transporting such tools through the inside of the pipeline have a tendency to tip or otherwise spiral within the pipeline as they travel along the pipeline. To provide the accuracy required for internal pipeline inspection, it is important to be able to maintain a fixed radial orientation while traveling through the pipe. Any imbalance in the conveyance apparatus seen by the payload can cause it to ride up the pipe wall. This, in turn, can cause the payload carriage to spiral as it moves through the pipe and, in some instances, may even cause the payload carriage to become immobilized if it flips over. This spiraling is avoided by ensuring that the payload carriage follows the “valley” or lowest point of the pipe interior as it travels through the pipe.